This invention relates in general to fluorinated dimethyl ethers, and specifically to bis(difluoromethyl)ether (CHF.sub.2 OCHF.sub.2), which have utility has CFC alternatives, particulary for use as refrigerants, blowing agents, etc.
Bis(difhoromethyl)ether has been prepared previously by chlorination of dimethyl ether followed by isolation and fluorination of bis(dichloromethyl)ether. The chlorination step resulted in a complex mixture of chlorinated dimethyl ethers, some of which were unstable, e.g. to distillation, from which bis(dichloromethyl)ether was separated. Moreover, chloromethyl methyl ether and bis(chloromethyl)ether are produced by this reaction, and are carcinogens.
Another approach to the synthesis of methyl difluoromethyl ether is disclosed by Hine and Porter in Methylene derivatives as intermediates in polar reaction VIII. Difluoromethylene in the Reaction of Chlorodifluoromethane with Sodium Methoxide, published in the Journal of the American Chemical Society 79, 5493-6 (1957). This article describes a reaction mechanism wherein the desired difluoromethyl-methyl-ether is synthesized in a batch reaction in a fixed ratio with the by-product trimethyl-orthoformate, while continuously refluxing the unreacted feed. However, not only does this reaction produce large amounts of trimethylorthoformate, but also the product itself breaks down to trimethylorthoformate, resulting in less than advantageous yields of the desired difluoromethyl methyl ether.
U.S. Pat. No. 5,185,474, the disclosure of which is hereby incorporated by reference, discloses avoiding the production of such carcinogens and unstable compounds by using methyl difluoromethyl ether as a starting material. The methyl difluoromethyl ether is chlorinated to produce a reaction mixture including at least one compound of the formula CF.sub.2 HOCH.sub.3-z Cl.sub.z, wherein z is 1, 2, or 3. The mixture can then be fluorinated, or any one of the chlorination compounds first separated from the mixture and separately fluorinated.
However, unreacted starting material (difluoromethyl methyl ether) and a by-product (chlorofluoromethane) formed in the preparation of bis(difluoromethyl)ether, remain as impurities in the product after distillation. They cannot be completely removed during distillation in view of the proximity of their boiling points to that of bis(difluoromethyl)ether, or possibly in view of the unconfirmed formation of an azeotrope. The presence of these impurities in bis(difluoromethyl)ether can deleteriously effect its performance as a refrigerant, for example. Moreover, chlorofluoro-methane is a known carcinogen.
Accordingly, it is therefore an object of the present invention to provide purified bis(difluoromethyl)ether.
It is an further object of the present invention to provide a process for the production of purified bis(difluoromethyl) ether.